Human B cells go through a variety of processes that are classified based on the kind of surface antigens being expressed, and finally mature into antibody-producing plasma cells. At the final stage of their differentiation, B cells, on one hand, acquire the ability of producing cytoplasmic immunoglobulins and, on the other, B cell-associated antigens such as cell surface immunoglobulins, HLA-DR, CD20, Fc receptors, complement C3 receptors and the like disappear (Ling, N. R. et al., Leucocyte Typing III (1986) p320, Oxford, UK, Oxford).
So far, there have been reports on monoclonal antiboies such as anti-PCA-1 (Anderson, K. C. et al., J. Immunol. (1983) 130, 1132), anti-PC-1 (Anderson, K. C. et al., J. Immunol. (1983) 132, 3172), anti-MM4 (Tong, A. W. et al., Blood (1987) 69, 238) and the like that recognize antigens on the cell membrane of the plasma cells. However, anti-CD38 monoclonal antibody is still being used for detection of plasma cells and myeloma cells (Epstein, J. et al., N. Engl. J. Med. (1990) 322, 664, Terstappen, L. W. M. M. et al., Blood (1990) 76, 1739, Leo, R. et al., Ann. Hematol. (1992) 64, 132, Shimazaki, C. et al., Am J. Hematol. (1992) 39, 159, Hata, H. et al., Blood (1993) 81, 3357, Harada, H. et al., Blood (1993) 81, 2658, Billadeau, D. et al., J. Exp. Med. (1993) 178, 1023).
However, anti-CD38 monoclonal antibody is an antigen associated with activation of T cells rather than an antigen associated with differentiation of B cells, and is expressed on various cells in addition to B cells. Furthermore, although CD38 is not expressed on some of the lymphoplasmacytoid, it is strongly expressed on the hemopoietic precursor cells. For these reasons, it is believed that anti-CD38 monoclonal antibody is not suitable for research on differentiation and maturation of human B cells or for treatment of diseases of plasma cells.
Goto, T. et al. have reported mouse anti-HM 1.24 monoclonal antibody that recognizes an antigen having a molecular weight of 29 to 33 kDa which is specifically expressed on B cell lines (Blood (1994) 84, 1922-1930). From the fact that the antigen recognized by anti-HM 1.24 monoclonal antibody is believed to be associated with the terminal differentiation of B cells (Goto, T. et al., Jpn. J. Clin. Immun. (1992) 16, 688-691) and that the administration of anti-HM 1.24 monoclonal antibody to a plasmacytoma-transplanted mouse resulted in specific accumulation of the antibody at the tumor (Shuji Ozaki et al., The Program of General Assembly of the 19th Japan Myeloma Study Meeting, general presentation 3), it has been suggested that anti-HM 1.24 monoclonal antibody, by labelling with a radioisotope, may be used for diagnosis of tumor localization, the missile therapy such as radioimmunotherapy, and the like.
Furthermore, the above-mentioned Blood describes that the anti-HM 1.24 monoclonal antibody has the complement-dependent cytotoxicity activity to the human myeloma cell line RPMI8226.
Myeloma is a neoplastic disease characterized by the accumulation of monoclonal plasma cells (myeloma cells) in the bone marrow. Myeloma is a disease in which terminally differentiated B cells that produce and secrete immunoglobulins, or plasma cells, are monoclonally increased mainly in the bone marrow, and accordingly monoclonal immunoglobulins or the constituting components thereof, L chains or H chains, are detected in the serum (Masaaki Kosaka et al., Nippon Rinsho (1995) 53, 91-99).
Conventionally chemotherapeutic agents have been used for treatment of myeloma, but there have been found no effective therapeutic agents that can lead to remission of myeloma and elongation of the survival period of patients with myeloma. There is, therefore, a long-awaited need for the advent of drugs that have a therapeutic effect on myeloma.
Mouse monoclonal antiboies have high immunogenicity (sometimes referred to as “antigenicity”) in humans. Accordingly, the medical therapeutic value of mouse monoclonal antibodies in humans is limited. For example, a mouse antibody administered into a human may be metabolized as a foreign substance so that the half life of the mouse antibody in the human is relatively short and thereby it cannot fully exhibit its expected effects. Furthermore, human anti-mouse antibodies that are raised against the administered mouse antibody may trigger immunological responses that are unfavorable and dangerous to the patients, such as serum disease, other allergic reactions, or the like. Therefore, mouse monoclonal antibody cannot be frequently administered into humans.
In order to resolve these problems, a method was developed for reducing the immunogenicity of non-human-derived antibodies such as mouse-derived monoclonal antibodies. As one such example, there is a method of producing a chimeric antibody in which the variable region (V region) of the antibody is derived from the original mouse and the constant region (C region) thereof is derived from an appropriate human antibody.
Since the chimeric antibody thus obtained contains the variable region of the original mouse antibody in the intact form, it is expected to bind to the antigen with a specificity identical to that of the original mouse antibody. Furthermore, in a chimeric antibody the ratio of the amino acid sequences derived from non-humans is substantially reduced, and so the antibody is expected to have a low immunogenicity compared to the original mouse antibody. A chimeric antibody may bind to the antigen in an equal manner to the original mouse monoclonal antibody, and may include immunological responses against the mouse variable region though the immunogenicity is reduced (LoBuglio, A. F. et al., Proc. Natl. Acad. Sci. USA, 86, 4220-4224, 1989).
The second method for reducing the immunogenicity of mouse antibody, though much more complicated, can reduce the potential immunogenicity of mouse antibody further greatly. In this method, only the complementarity determining region (CDR) of the variable region of a mouse antibody is grafted to the variable region of a human antibody to prepare a “reshaped” human antibody variable region.
However, In order to make the structure of the CDR of a reshaped human antibody variable region as much close as possible to that of the original mouse antibody, if necessary, part of the amino acid sequence of the framework region (FR) that supports the CDR may be grafted from the variable region of the mouse antibody to the variable region of the human antibody. Subsequently, this V region of the humanized reshaped human antibody is linked to the constant region of a human antibody. The part that is derived from the non-human amino acid sequence in the finally reshaped humanized antibody is the CDR, and only part of the FR. A CDR is composed of hypervariable amino acid sequences which do not exhibit species-specific sequences. Therefore, the humanized antibody carrying the mouse CDR should not have an immunogenicity stronger than the natural human antibody having the human antibody CDR.
For the humanized antibody, see Riechmann, L. et al., Nature, 332, 323-327, 1988; Verhoeye, M. et al., Science, 239, 1534-1536, 1988; Kettleborough, C. A. et al., Protein Engng., 4, 773-783, 1991; Meada, H. et al.; Human Antibodies and Hybridoma, 2, 124-134, 1991; Groman, S. D. et al., Proc. Natl. Acad. Sci. USA, 88, 4181-4185, 1991; Tempest, P. R. et al., Bio/Technology, 9, 266-271; 1991; Co, M. S. et al., Proc. Natl. Acad. Sci. USA, 88, 2869-2873, 1991; Carter, P. et al., Proc. Natl. Acad. Sci. USA, 89, 4285-4289, 1992; Co, M. S. et al., J. Immunol., 148, 1149-1154, 1992; and Sato, K. et al, Cancer Res., 53, 851-856, 1993.
Queen et al. (International Application Publication No. WO 90-07861) describes a method for producing a humanized antibody of an anti-IL-2 receptor antibody Anti-Tac. However, it is difficult to completely humanize all antibodies even following the method as set forth in WO 90-07861. Thus, WO 90-07861 does not describe a general method for humanizing of antibodies, but merely describes a method for humanizing of Anti-Tac antibody which is one of anti-IL-2 receptor antibodies. Furthermore, even when the method of WO 90-07861 is completely followed, it is difficult to make a humanized antibody that has an activity completely identical to the original mouse antibody.
In general, the amino acid sequences of CDR/FR of individual antibodies are different. Accordingly, the determination of the amino acid residue to be replaced for the construction of a humanized antibody and the selection of the amino acid residue that replaces said amino acid residue vary with individual antibodies. Therefore, the method for preparing humanized antibodies as set forth in WO 90-07861 cannot be applied to humanization of all antibodies.
Queen et al. Proc. Natl. Acad. Sci. USA, (1989) 86, 10029-10033 has a similar disclosure to that of WO 90-07861. This reference describes that only one third of the activity of the original mouse antibody was obtained for a humanized antibody produced according to the method as set forth in WO 90-07861. In other words, this shows that the method of WO 90-07861 itself cannot produce a complete humanized antibody that has an activity equal to that of the original mouse antibody
Co et al., Cancer Research (1996) 56, 1118-1125 was published by the group of the above-mentioned Queen et al. This reference describes that a humanized antibody having an activity equal to that of the original mouse antibody could not be constructed even by the method for making humanized antibody as set forth in WO 90-07861. Thus, the fact not only reveals that the method of WO 90-07861 itself cannot produce a complete humanized antibody having an activity equal to the original mouse antibody, but that the method for constructing humanized antibody as set forth in WO 90-07861 cannot be applied to humanization of all antibodies.
Ohtomo et al., Molecular Immunology (1995) 32, 407-416 describes humanization of mouse ONS-M21 antibody. This reference reveals that the amino acid residue which was suggested for humanization of the Anti-Tac antibody in WO 90-07861 has no relation with the activity and the method as set forth in WO 90-07861 cannot be applied.
Kettleborough et al, Protein Eng. (1991) 4, 773-783 discloses that several humanized antibodies were constructed from mouse antibody by substituting amino acid residues. However, the substitution of more amino acid residues than were suggested in the method of humanization of the Anti-Tac antibody as described in WO 90-07861 was required.
The foregoing references indicate that the method of producing humanized antibodies as set forth in WO 90-07861 is a technique applicable only to the Anti-Tac antibody described therein and that even the use of said technology does not lead to the activity equal to that of the original mouse antibody.
The original mouse antibodies described in these references have different amino acid sequences from that of the Anti-Tac antibody described in WO 90-07861. Accordingly, the method of constructing humanized antibody which was able to be applied to the Anti-Tac antibody could not be applied to other antibodies. Similarly, since the mouse anti-HM 1.24 antibody of the present invention has an amino acid sequence different from that of the Anti-Tac antibody, the method of constructing humanized antibody for the Anti-Tac antibody cannot be applied. Furthermore, the successfully constructed humanized antibody of the present invention has an amino acid sequence different from that of the humanized Anti-Tac antibody described in WO 90-07861. This fact also indicates that the same method cannot be applied for humanization of antibodies having different CDR-FR sequences.
Thus, even if the original mouse antibody for humanization is known, the identity of the CDR-FR sequence of a humanized antibody having an activity is confirmed only after trial and error experiments. WO 90-07861 makes no mention of the FR sequence which is combined in the humanized antibody constructed in the present invention and of the fact that an active humanized antibody could be obtained from the combination with FR, much less the sequence of the CDR.
As hereinabove mentioned, humanized antibodies are expected to be useful for therapeutic purposes, but humanized anti-HM 1.24 antibody is not known or not even suggested. Furthermore, there is no standardized method available that could be generally applied to any antibody for production of a humanized antibody, and a variety of contrivances are needed for constructing a humanized antibody that exhibits sufficient binding activity, binding inhibition activity, and neutralizing activity (for example, Sato, K. et al., Cancer Res., 53, 851-856, 1993).